Pilot channel for telegraph systems



Nov; 3, 19.31.

J. HERMAN PILOT CHANNEL FOR TELEGRAPH SYSTEMS Filed Feb. 25. 1950Filtelzs' .De tector .5

Iow Pass Filter INVENTOR J. flI MWW ATTORNEY by-the winding will thenbegreaterthan that produced by the winding- 3 causing the armature ofthe relay W to close its contact 9%. In that event the negativeterminalofa batterymay be connected to the local telegraph'receivingcircuit. If the windings m and 3 have the same number of turns, and ifthe armature of the relay W is mechanically unbiased, then it is thepractice in the art to arrange the circuit so that twice as much curm'aybe connected to? the :positive side of the battery used in the detectorD for'the purpose of receiving signals withouttheaid of a pilot channel.

The winding m of an additional polar relay W is in series with thewlnding m of.

the. relay W and the plate current of the tube of the detector'D flowsequally through both of thesewindings. The Winding 3 of relay "Wisconnected in the plate circuit of a vacuum tubedesrgnated V, thisplate circuit including battery B 'windm'g 3 a meter M the plate and'fi'lament electrodes of tube .V and ground. Win'ding y is'so arrangedthat the current flowing intheplate circuit of the tube .V iwill causeit toproduce a mag V neticef i'ect upon the armature of the relay whichopposes the magnetic efiect pro- "distant station isso-heldythe value ofthe :current flowing through meter My may be changed .to any desiredextent by the adjustduced by thewind'ingzw when current flows in theplate circuit of the tube of the detector D: The armature and markingcontact an ofthe relay TN are employed for the purpose of controllingthe potential of the grid electrode of-the vacuum tube V in a mannerwhich will be described in greater detail herein' after.

"When th e telegraph key at the distant sendingstation corresponding tothe channel, I under consideration 'isheld in its closed' post' tron, asubstantially steady current will-flow through the plate circuit of thetube forming de'tector D and this current may be read on the meter MWhen the telegraph key at the inent of the potentiometershown-associated withthe detector ll When the telegraph key 1s beingoperated for the transmission of signals, the Ineterh l will no longerindicate the actual value of the current in the plate circuit of thetube forming detector 1), but the pointer V of this meter will followthe-signals and it will tend to; give an intergradedreading of thecurrent lmp'ulses in the circuit.

One of the principal featuresof this" invention lies in theprovision ofthe meter i. 2

for the purpose of indicating the maximumivalue'of the current in theplate circuit of the tube of the detector 1), even when teleigraphsignals are being transmitted. Iii

. may have a capacity of about 4 microiarads, 80

the telegraph key at the distant station is kept closed, the current inthe plate circuit of the tube V above described which includes thewinding 3 will be less than the steady the armature and. marking contactm otrelay N and aresistance R which may have a value of, for example,100,000 ohms. Before the closure of contact am a condenser C,wh1ch wascharged to a negative potential bya battery B through a resistance R3,which may have value of, for example 2 niegchms. But upon the closure ofcontact m 'the condenser C becomes gradually discharged hrcughresistance lt the armature and contaggs m of relay Vi a and ground.

full voltage of battery B it will so bias the grid electrode or thevacuum tube V, with respecttothe filament electrode thatpracticallynoc'urrent will flow intheiplate ,circuit of the vacuum tube. B. ,But uponreduction of the'chargeiupon condenser C, the grid electrode will becomeless negatively biased and substantially greater current will flow inthe plate circuit of the vacuum tube V." Upon theolosureot the contact mof the relaythe'condenser C does become discharged, and hence the flow.of current from the battery 3 in :the plate circuit or c the; vacuumtube V-wi-ll increase and will continue-to increase,Wll-llfitll'COIltflCt m r mains closed, untll' the magnetic effect of Vwinding 2 1 becomes suiiicient to overcome the corresponding eii'ectproduced by the windingw The armature. of the relay W Will then movetoithe s contact. As soon as this occurs, thedischarging circuit ofcondenser C; which includesthe resistance R will. be'openedand thebattery'lS will further increase the charge on condenser C throughresistance R As the condenser G becomes charged to agreater negativevoltage, less current will flow through winding. fg of relay W and thecurrent lnwmding 3 will decrease and continue to decrease until themagnetic eiiect produced by winding 3 becomes less than that produced bywindmg 09 The armature of relay W3 will then 'again'operate so as toclose contact m in order LO decrease the'charge of condenser C. Thisprocess Wlll be repeated and the armature-oi? the relay W will move backand forth between itsicontacts as a result of only slight changes in thecurrent in the plate circuit or" the tube V.

W lt will be evident that if the windings 00 and 311 have an equalnumber.of'turns, and fl'i the armatureot the relay 'VV- 1s not mevVhen thecondenser 'Cis charged to the chanically biased, the operation 'of thear-f rangement will resultiin'a fairly steady value of'current throughthe windingj 'and this current will be substantially equal to thatflowing throughwinding' a. It the ratio of the numbers of turnsinithewindings m and 3 is not unity, then the values of the currents in thesetwo "windings-will be in-,

versely proportional to their' -respective num-- bers of turns. Thevalue of the current in. the plate circuit of the tube of the detector Dmay readily be determined from the value of the current in the platecircuit of the tube V as indicated by the. meter M and the lattencurrent will be substantially constant.

. Because of the large time constant of the charging. circuit of.condenser G established through resistance R -,and because of therelatively-small time constant of the discharge its'normal value.

In connection with a channel over which k printers may be operated, theopening of the sending contacts for a length of time which may giveafalse indication of detector current, willo'ccur only when the circuitmay be. in trouble. In connectionwith the channel operated by manualMorse the key'may be held open for an appreciablelength of time, and inthat case the arrangement may occasionally give a false indication. Sucha condition will be apparent to an experienced attendant and he will notbe disturbed.

The characteristic of the detector which 'may be used in the operationofa carrier normal value of the detector current.

telegraph: system of the type described is usually such that fairlylarge changes in the transmission equivalent of the circuit may produceonly a small change in this t. may be advantageous to use separatedetectors for the relays W and 'VV Such detectors may be connected inparallel with each other across the output circuit of the i in the pilotchannel maybe used to prevent Fig. 2 of the drawings represents anarrangement by which the current provided bias in the signals resultingfrom changes in the transmission equivalent of the line. -Here line L isbridged by a plurality'offilters 1 ,33 F13, and F157 COnneCted inparallel relationship, and these are connected to detectors D D D D andD respectively. The detector D of the pilot channel is connected-inparallel with the detector D across the output circuit of the filter F li i The pilot arrangement includes a relay W and thevacuum tube V whichare interconnected the same as shown in Fig. lot the drawings. Thebattery B is bridged by all of the resistance of the potentiometer P andthe movable arm of this potentiometer extends to the axis of thearmature of relay N A low-pass filter is connected between the upperterminal of the biasing winding of relay VV and the plate electrode ofthe vacuum tube V, as shown, this filter including series inductances E,which may be of equal magnitude, and shunt -condensersC which may haveequal capacities. This lowpass filter is intended to smooth out smallvariations in the plate current of the tube V resulting from theoperation of the armature of relay N It is to be noted that the platecurrent of tube V flows through a circuit which includes the windings Eof the low-passfilter, the winding of a milliammeter. relay Q, thebiasing windings of relays W W W14, V and W battery B and ground. Itwillbe apparentv that upon adjustment of the gain of the detector D theproper value of thebiasing current may be initially obtained for'normalline conditions. When the transmission equivalent of the line'changes,the current through the biasing windings of the various relays will becorrespondingly changedand thereby will prevent bias in the telegraphsignals.

The resistance R forms a leak circuit which includes the battery B thebiasing winding of relay VV the biasing windings 'of 'relays- N Vi a, 12and l V sistance R and ground. Since the channel to which detector D isconnected may be held open for an appreciable length of time by localcircuit troubles, current in the leak circuit will prevent the reductionin thefio'w of current through the biasing windings oi the variousrelays to zero. The effect ofthe current in the leak circuit is such asto establish a minimum value for the current through these biasingwindings, which the battery B of the pilot circuit may supply. A similareffect may be obtained by reducing the voltage of the grid battery B sothat a small,

though definite value 0t plate currentwill flow even when the armatureof relay W closes its 'spacmg contact a. A limit tothe upper value ofthe current mthe plate circuit of the tube V may be obtained bysetting'the movable arm of the potentiometer P ata suitablepoint.

The armature of the milliammeter'relay Q may move between two contactsboth of which are connected to a bell G and a battery B which are inseries with each other.

When the current through the winding of relay Q, exceeds a predeterminedvalue, one ofitscontacts will be closed, and its other contact will beclosed when the value of they currentdrops below another predeterminedvalue.- In either case an alarm will be sound- 7 ed by the bell Gbecause of the flowof current from its associated battery B l WVhilethis invention has been shown in certain particular arrangements merelyfor V of the appended claims.

What is claimedis:

1'.' The method of maintainingthe amplitude of a direct current.flowingf through one windingof apolar relay substantiallyequal to themaximum amplitude of signaling current flowing through another windingof said relay which consists in progressively and gradually increasingthe current periodically "through the first of said windings until itexceeds the maximum amplitude of the signaling current flowing throughthe other of said windings, and progressively and gradually decreasingthe current periodically through the first of said windings until it isless-than the maximum. amplitude of the ."signaling current flowingthrough the other of said; windings.

" The method of continuously maintaining the amplitudeof a directcurrent flowing through the biasing winding of a polar relaysubstantially equal to the maximum amplitude of signaling currentflowing through another winding of said relay, which consistsinprogressively and periodicall decreasing the current through saidbiasing winding until its armature closes one of its contacts, andprogressively and periodically increasing ,the'currentthrough saidbiasing winding unt1l1ts armature closes the other of its contacts. 1 V

3 The combination ofa relay having first and second windings bothcapable of operating its armature in-mutually'opposite directions, meansfor transmitting pulses of direct current representing signals throughthe first or said windings, a source of direct cur rent individual tothe second of the windings of said relay, and means associated with thearmature ofsaid relay for periodically increasing'the flow of currentthrough the secondofsaid windings the amplitude of that currentdropsbelow the maximum amplitude of the current through the first ofsaid windings and for periodically decreasing the flow of currentthrough the second of said windingsas it rises above said maximumamplitude. 7' r 4. The combination of a signaling source, a relay havingtwo windings oneof which is connected to said signaling source, meansfor transmitting direct current through the other winding of said relay,a circuit controlled bythe armature of said relay, means associatedwith, said circuit to change the magnitude of the current flowingthrough said other winding of sa d relay inaccordance with changesin themaximum value of the current flowing from said signaling source. I

5. The'comb-ination of a vacuum tube hav ing plate, filament and gridelectrodes, a first source of direct current potential, a polarizedrelay the winding of which is 0011-, nected between the plate'andfilament electrodes of said vacuum tube through said first source ofdirect current,-a condenser. connected between the grid and filamentelec-' trodes of said vacuum tube, a second source of direct currentpotential, a first resistance connected in series with said secondsource of direct current potential between the grid and filamentelectrodes of said vacuum tube, and a second resistance connected inseries with the armature and contact ofsaid relay between the grid andfilament electrodes of said vacuum tube. V v

6. The combination ota vacuum tube having plate, filament and gridelectrodes, a first source of directcurrent potential, a, polarizedrelay having two windings through one of which pulses of direct" currentflow, the other of the windings of said relay being'connected betweenthe plate 'and'filament elec-- trodes of said vacuum tube throughsaid'first source of direct current potential, means for indicating themagnitude of the current through the latter winding ofsaid relay, acondenser connected between 'thegrid and filament electrodes of saidvacuums tube, a second source of-direct current potential, a first resisance connected in series with said second source of direct currentbetween the grid and filament electrodes of said vacuum tube, and asecond resistance connected'in series with the armature and one contactof said relay between the grid and filament electrodes ofthe vacuumtube.

'7. A system for the prevention of bias in signals transmitted over aline which result "from changes in the transmission equivalent oi theline comprising a. polar relay having two wlndin-gs, an auxiliary polarrelay also having two" windings, signals impressed on the line causingcurrents to flow through one of the windings of each of said relays,biasing current flowing through the other of the windings of each ofsaid relays, and means associated with said auxiliary relay to changethe biasing current in accordance with amplitude 01" the a line,aplurality of polar relays eachof '7 which has first andsecond windings,means whereby the signaling currents flowing over said line becomeimpressed upon the first windings of said relays, a source of'biasingcurrent connected'in series Withthe second windings of said'relays,:andmeans controlled by the armature of one of said relays to r 5 change thebiasing current in accordance With variations in the maximum amplitudeof the w signaling current. y

I In testimony whereof, I have signed my name to this specification this24th day of February, 1930. a v JOSEPH HERMAN.

